But a bare bones one to get you thinking about what the story/book really is about could be like this:

Who is the book about? This is your main character. Protagonist. Jot down the name, age, gender (or transgender), and what makes them “them”–their occupation or special talent (psychic or world’s best embroiderer) or status (genius, rich, poor, ex-con, homeless, divorcing) or anything that is intriguing, especially if it’s genre-specific. Do they have quirks? Think of strong adjectives! How would you describe them in two or three words if you had to? Hermit theologian; cowardly army sergeant; alcoholic pilot; autistic schoolboy; kickboxing nun–all of these would catch my attention in a blurb.

What do they need/want and why? This covers the protagonist’s goal and motivation. They must have one big one (and probably lesser ones). Katniss first wanted to save her sister by substituting for her in the Hunger Games; then she wants to save herself and Peeta: survival!

Where is the story happening? Setting. This is very important for some novels and non-fiction books, so important that the title may derive or include the setting, such as with Dune or Bury My Heart at Wounded Knee or The Bridges of Madison County.

What is the story problem? If it’s a novel (I mostly discuss novels here, so expect that as my default), you must have conflict, a problem, an obstacle, trials, enemies or villains or something in the way of what the protagonist wants (be it internal or external, or, ideally, both). There may be many conflicts and issues, but what is the main one that propels your tale. If it’s non-fiction, what is the problem the book solves: how to simplify a complicated life; how to stop overspending; how to find a mate; how to stop overeating; how to write a book when you don’t know where to start.

Who or what is obstructing or antagonizing the main character? You may have already named this in answering the previous question. It could be the serial killer taunting the homicide detective. It could be cancer killing the protagonist. It could be the hostile environment of an alien planet making survival difficult. It could be an evil cadre of powerful lawyers out to ruin the rookie lawyer-protagonist’s first big case. Name the nemisis, villain, obstacle.

What are the stakes? If the character fails, what is the consequence? It might be that the man she loves gets away or the aliens win the war against the humans or the defendant goes to prison for life or a he loses his family’s farm or she dies in the imperial games. Stakes. Consequences.

Who are the allies or other important characters? You can’t think of Katniss without Peeta, Romeo without Juliet, Bella without Edward and Jacob, Bridget Jones without Mr. Darcy, Elizabeth Bennet without Mr. Darcy, or Clarice Starling without Hannibal Lecter. Most novels have important secondary characters who assist the main character or who are intricately involved in the progress of that character–as they affect each other.

What is the genre and tone of the work, and its audience? Is it a YA Fantasy Romance? Is it a Dark CIA Thriller? Is it an intellectual science fiction adventure for adults? Is it a religious romance aimed at Christian women who don’t want sex scenes? Is it a literary novel about a group of chess players in Central Park, all former vets dealing with regrets and traumas through game strategy? The tone of the blurb ideally should relate to the tone of the book–whether suspenseful, funny, youthful, or wise. And you would likely use different diction for one aimed at teens than one aimed at an older audience.

What is the story question? We’ve all seen blurbs that end with questions–seen that a lot. Blurbs don’t have to end in questions or ever have any question within them. But this really is a natural feeling strategy. Only reading the book will answer that question. It’s bait. They are too useful to be discarded as old school. Will Katniss win the Hunger Games? Will Clarice capture Buffalo Bill? Will the kids from The Glade make it through The Maze alive? Will Romeo and Juliet be able to live happily ever after? Will the astronaut on Mars survive? (And yes, The Martian back cover copy ended with a question about survival. It didn’t hurt sales, huh?)

What you don’t need:

The ending–You aren’t going to give it away.

Secondary plots–That’s not what’s going to nab the reader. The main storyline is.

Names of characters who aren’t very important–Plot movers and shakers only. In a romance, you have a hero and a heroine (though you might have an antagonist to name in a romantic suspense). In some blurbs, you’d only name one character: the protagonist.

Most of the middle and latter part of your story–I’ve seen recommendations from some editors to gather blurb material from the first 15% of your book: act one. I won’t say that applies all the time, but that’s the part of the book that you’ve shaped to hook a reader. It makes sense that it’s where you find most of your blurb: your character (ordinary world), inciting incident, perhaps main ally and antagonist, the big need or goal, the story question.

There you go. You’re ready to begin scribbling down the preliminary notes for your blurb’s first draft.

I recommend you do this too: grab some books from your personal shelves or head to Amazon and bring up the pages for ebooks you’ve bought. Read the blurbs. Get a sense of the forms used, the tones, and notice the key elements that sold you.